Component alignment is of critical importance in fiber optic, semiconductor laser and/or MOEMS (micro-optical electromechanical systems) based system manufacture. The basic nature of light requires that light generating, transmitting, and modifying components must be positioned accurately with respect to one another, especially in the context of freespace-optical systems, in order to function properly and effectively in electro-optical or all optical systems. Scales characteristic of fiber optic, semiconductor laser, and MOEMS devices can necessitate micrometer to sub-micrometer alignment accuracy.
Consider the specific example of coupling light from a semiconductor diode laser, such as a pump or transmitter laser, into the core of a single mode fiber. Only the power that is coupled into the fiber core is usable. The coupling efficiency is highly dependent on accurate alignment between the laser output facet and the core; inaccurate alignment can result in partial or complete loss of signal transmission through the optical system.
Other more general examples include optical amplification, receiving and/or processing systems. Some alignment is typically required between an optical signal source, such as the fiber endface, and a detector. In more complex systems including tunable filters, for example, alignment is required not only to preserve signal power but also to yield high quality systems through the suppression of undesirable spatial optical modes within and without the systems.
Generally, the manufacture of high performance devices typically involves active alignment strategies. An optical signal is transmitted through the components and detected. The alignment is performed based on the transmission characteristics to enable the highest possible performance level for the system. Nonetheless, even with these techniques for active alignment, there is still the requirement that the optical components be first installed accurately and with precision relative to other components.
The general mechanism for precisely positioning these optical components on the optical submount or bench is to match alignment features on the optical components with alignment features on the optical benches. Older systems utilized the outer edges of the optical components as the alignment features. Typically, however, these outer edges are subject to variability due the manufacturing process and the subsequent handling of the components prior to installation. Moreover, the position of these outer edges relative to an optical axis, for example, can be highly variable if the optical components are coated with a material to enhance bonding, for example, prior to installation.
A parallel objective in optical system manufacture is to automate manufacturing processes. Modern precision placement machines such as flip-chip bonders typically have integrated vision systems that allow for the location of the bench/submount and component alignment features to automate the optical component installation process to some degree. These vision systems, however, are highly susceptible to spatial or surface noise that could give rise to ambiguity as to the precise location of the alignment features.
In general, according to one aspect, the invention concerns an optical component adapted for attachment to an optical bench or submount. The optical component has an alignment feature that is used in the positioning of the optical component relative to the optical bench. This alignment feature is formed in an exterior wall of the optical component. Further, according to the preferred embodiment, the alignment feature has a re-entrant sidewall. This last characteristic facilitates the identification of a precise location of the component by a vision system, for example, thus, allowing the accurate placement and installation of the optical component on the optical bench.
According to a current embodiment, the alignment feature is formed in a bottom face of the optical component. This configuration is appropriate for flip-chip bonders, providing bottom-to-top alignment. In other implementations, the features can be located on a top face in the case of top-to-top alignment.
Moreover, according to a preferred embodiment, a proximal origin of the exterior wall surrounding the alignment feature is depressed relative to an outer exterior wall. Specifically, a proximal origin of the reentrant sidewall is depressed relative to the exterior wall surrounding the alignment feature. This aspect of the preferred embodiment is particularly helpful since it is this proximal origin of the reentrant sidewall that is used as the focal plane for the vision system. Since the origin is depressed relative to the surrounding walls, there is an opportunity to defocus the adjacent exterior wall. This defocusing removes a major source of noise to the vision system, which are the grain boundaries in the bulk material of the component, when made of metal, for example, or surface roughness generally.
It is not uncommon for these optical components, especially when they are manufactured using lithographic and plating processes, to have relatively large grain sizes, on the order of 10-100 micrometers, relative to the overall size of the component, e.g., 100-2000 micrometers, and the desired placement tolerances of 1 to 20 micrometers. Grain boundaries can be further decorated, or highlighted, in plating processes preceding the installation. According to the present invention, however, such grain boundaries or surface roughness can be defocused allowing a vision system to more accurately identify or locate the alignment features.
In one implementation, the exterior wall surrounding the alignment feature is bonded to the optical bench. In another implementation, however, this exterior wall is depressed relative to a surface that forms the bonding surface.
In the current implementation, the alignment feature comprises a slot that extends along the length of the optical component. Particularly, the slot typically extends along an entire length of the optical component.
In the preferred embodiment, the bonding process is compatible with carrier-class optical equipment. Thus, the optical components are preferably solder bonded to the optical bench. As such, they are preferably coated with, for example, a gold or gold alloy, to a thickness of between 0.5 and 4 micrometers. Currently, they are plated to about 1.25 micrometers thick. Such coatings can be either sputtered or plated onto the optical component.
Further, according to the invention, multiple alignment features are spaced along the width of the optical component. Preferably, these alignment features have different widths relative to each other such that the particular alignment feature""s location on the optical component can be determined by reference to the alignment feature""s width. In the current implementation, the optical alignment features of the optical components are used to place the optical components on the bench. Presently, they are placed on the bench with an accuracy of better than 10 micrometers in the preferred embodiment. Particularly, when the placement processes have been optimized, placement accuracies of better than one to two micrometers are attainable.
As such, the alignment features are relatively small. Presently, they are between 10 and 100 micrometers wide. If they are not plated or otherwise coated, however, relatively smaller alignment features of less than 50 micrometers can be used. Presently, the alignment features have waists of about 25 micrometers when no plating is used, whereas waists of about 50 micrometers are used in conjunction with alignment feature coating.
In general, according to another aspect, the alignment features comprise two opposed reentrant sidewalls. This configuration in one implementation results in a frusto-triangular profile. In another implementation, an hourglass profile is used. In each case, the waist, or narrowest portion between the sidewalls, of the alignment features is generally between 10 and 100 micrometers.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.